Less than 1 month –
Less than 10 hrs/week –
MicroSIP - open source portable SIP softphone based on PJSIP stack for Windows OS.
It allowing to do high quality VoIP calls (person-to-person or on regular telephones) via open SIP protocol. From cloud of SIP providers you can choose best for you, register account and use it with MicroSIP. You'll get free person-to-person calls and cheap international calls.
Main in MicroSIP:
small footprint (>2.5MB) and RAM usage (>5MB) - written in C and C++ with minimal possible system resources usage ...